The use of ophthalmic lenses for the correction of ametropia is well known. For example, multifocal lenses, such as progressive addition lenses ("PAL's"), are used for the treatment of presbyopia. The surface of a PAL provides far, intermediate, and near vision in a gradual, continuous progression of vertically increasing dioptric power from far to near focus, or top to bottom of the lens. PAL's are appealing to the wearer because PAL's are free of the visible ledges between the zones of differing dioptric power that are found in other multifocal lenses, such as bifocals and trifocals.
However, an inherent disadvantage in PAL's is unwanted lens astigmatism, or an astigmatism introduced or caused by one or more of the lens surfaces. Generally, unwanted lens astigmatism corresponds approximately to the near vision dioptric power of the lens. For example, a PAL with 2.00 diopter near vision power will have about 2.00 diopters of unwanted lens astigmatism. Additionally, the lens area free of unwanted astigmatism when the wearer's eye scans from the distance zone to the near zone and back is very narrow.
Any number of lens designs have been tried in attempting to overcome these disadvantages. However, although the state-of-the-art progressive lens designs provide some minimal decrease in unwanted lens astigmatism, large areas in the lenses' peripheries still are unusable due to unwanted astigmatism. Thus, a need exists for a PAL that overcomes some of the problems inherent in prior art PAL's.